US4463425A - Period measurement system - Google Patents

Period measurement system Download PDF

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US4463425A
US4463425A US06/281,163 US28116381A US4463425A US 4463425 A US4463425 A US 4463425A US 28116381 A US28116381 A US 28116381A US 4463425 A US4463425 A US 4463425A
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Prior art keywords
peak
period
biosignal
autocorrelation function
computation
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US06/281,163
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English (en)
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Toshinori Hirano
Masakazu Murase
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Terumo Corp
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Terumo Corp
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Priority claimed from JP9782080A external-priority patent/JPS5722736A/ja
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343—Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4362—Assessing foetal parameters
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/024—Detecting, measuring or recording pulse rate or heart rate
    • A61B5/02411—Detecting, measuring or recording pulse rate or heart rate of foetuses
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G—PHYSICS
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F10/00—Apparatus for measuring unknown time intervals by electric means
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S128/00—Surgery
    • Y10S128/92—Computer assisted medical diagnostics

Definitions

  • This invention relates to a period measurement system for measuring the period of a biosignal, particularly of a signal representative of the heartbeat of a fetus.
  • a conventional system for measuring the period of a biosignal relies upon a correlation system adapted to derive an autocorrelation function of the biosignal, and to measure the period of the biosignal of the basis of the autocorrelation function.
  • the period measurement system that relies upon the correlation system operates by sampling a biosignal over a suitable sampling period, computing the autocorrelation function of the biosignal from the sampled data, and detecting the peaks of the biosignal from the computed autocorrelation to thereby obtain the period.
  • the autocorrelation function indicates the similarity between two portions of the biosignal wave form at two different times separated by a certain time interval. In other words, it represents the degree of similarity of the repeating biosignal waveform. This can be better understood from FIG. 1, wherein it is seen that if a portion M 1 which repeats at a certain period T is shifted along the time axis by an interval of time which is equal to the period T, the portion M 1 will be superimposed on the immediately succeeding portion M 2 with maximum accuracy.
  • A( ⁇ ) in terms of the biosignal f(t) which is a function of the time t.
  • A(T) may be written ##EQU1## in which T represents the period of the biosignal and ⁇ represents a time interval between two points in time separated by a given interval, the earlier point in time being a reference time in connection with the biosignal.
  • ⁇ is a variable which applies a phase difference to the biosignal f(t) along the time axis.
  • FIG. 2 describes the conventional period measurement system that relies upon the correlation function to measure the period of a biosignal, specifically a signal representative of the heartbeat of a fetus, which signal will be referred to as a "heartbeat signal” hereafter.
  • a probe 2 is brought into contact with, say, the abdomen of a female subject to extract the fetal heartbeat signal for the purpose of measurement.
  • the heartbeat signal so detected has its waveform suitably processed in a preprocessing circuit 3 and then sampled at a predetermined sampling period in a sampling circuit 4.
  • the data obtained by sampling the heartbeat signal is stored in a data memory 6 composed of a plurality of shift registers. As each item of new data enters the data memory 6, items of data already stored up to that point are shifted to the immediately adjacent register, so that data is shifted sequentially from one register to another, with the oldest item of data in the last register being lost as each new input arrives.
  • a multiplier 8 and an adder 10 constitute an autocorrelation function computing circuit which is adapted to compute an autocorrelation function using the data stored in the data memory 6.
  • a correlation memory 12 stores the results of the computation, namely the computed autocorrelation function.
  • the autocorrelation function is computed by the multiplier 8 and the adder 10 on the basis of the data stored in the data memory 6.
  • the computation is performed on the basis of single sampling-cycle divisions and, for each item of data X 1 , X 2 , X 3 . . . , proceeds in the manner X 1 ⁇ X s+1 +A 1 ⁇ A 1 , X 1 ⁇ X s+2 +A 2 ⁇ A 2 , . . .
  • the arrangement is such that the phase difference variable ⁇ is varied in each single sampling cycle. It is therefore necessary to store in the correlation memory 12 the results of each and every autocorrelation function computation covering the entire body of data spanning the range over which the variable ⁇ is varied in each sampling cycle.
  • the correlation memory must have a very large storage capacity.
  • the computations described above are performed over a time interval corresponding to from two to three times the length of the period, so that much of this computation is without substantial meaning.
  • This fact also calls for a correlation memory of a large storage capacity and is also disadvantageous when viewed in terms of real-time processing owing to the fact that a large number of substantially meaningless computations are performed.
  • Another object of the present invention is to provide a period measurement system that enables correct measurement of the period by detecting true peaks, which correspond to the period of a biosignal, from a plurality of peaks obtained from an autocorrelation function.
  • the present invention provides a period measurement system comprising means for extracting a biosignal, autocorrelation function computation means for computing an autocorrelation function of the biosignal, peak detection means for detecting a peak from the autocorrelation functions, and period computation means for computing the period of the biosignal from that position on a correlation axis at which a peak is detected by the peak detection means, the computation of the autocorrelation function being continued for an interval corresponding essentially to the minimum value of the period of measurement, which interval begins with the detection of a peak, it being confirmed that no peak larger than the detected peak exists in the interval which corresponds to the minimum value and which begins with the detection of the peak, so as to detect that said peak is a true peak.
  • the autocorrelation function given by the equation ##EQU2## for a certain value of a variable ⁇ that applies a phase difference to the biosignal on the time axis, is computed in the autocorrelation function computation means for a specific value of the phase difference variable ⁇ , the specific value of the phase difference variable ⁇ is advanced on the time axis to conform to the progress of the sampling cycles, whereby the autocorrelation function computation means computes autocorrelation functions one after another corresponding to the new specific values of the phase difference variable, and the computed value of the autocorrelation function is stored in memory and compared to the most recent computed value of an autocorrelation function, so as to detect a peak.
  • FIG. 1 is a biosignal waveform diagram useful in describing measurement of a period by means of an autocorrelation system
  • FIG. 2 is a block diagram showing, in simplified form, the construction of period measuring apparatus to which the conventional system of period measurement is applied;
  • FIG. 3 is an illustrative view useful in describing the manner in which an autocorrelation function is computed in a period measurement system according to the present invention
  • FIG. 4 is a fetal heartbeat signal waveform diagram useful in describing a case where the period measurement signal of the present invention is appplied to measurement of the period between fetal heartbeats;
  • FIG. 5 is a waveform diagram useful in describing a system adapted to continue autocorrelation function computation for a fixed period of time following detection of a peak for the purpose of confirming whether or not the detected peak is a true peak;
  • FIG. 6 is a block diagram showing, in simplified form, the construction of a period measurement apparatus to which the period measurement system of the present invention is applied;
  • FIG. 7 is a block diagram useful in describing the storing of sampling data in a data memory, as well as the reading and later processing of the data;
  • FIG. 8 is a block diagram showing the detailed construction of a peak detector, peak level checking circuit and peak confirmation circuit included in the period measurement apparatus shown in FIG. 6;
  • FIG. 9 is a block diagram useful in describing the details of a reference level generator.
  • FIG. 3 is useful in describing a period measurement system in accordance with the present invention, and illustrates the system employed in computing the autocorrelation function of a biosignal.
  • Equation (3) means that the autocorrelation function of a biosignal is found by summing the product f(k)f(k+ ⁇ ) a total of n times by changing k, where f(k)f(k+ ⁇ ) is the product of sampled data f(k) and f(k+ ⁇ ) at two points in time separated by the phase difference variable ⁇ along the time axis.
  • the system adopted in the present invention computes an autocorrelation function for a certain value of the variable ⁇ , which applies the phase difference to the biosignal on the time axis in one sampling cycle of the biosignal, changes the value of the phase difference variable ⁇ along the time axis in conformance with the progress of the sampling cycles, and then computes an autocorrelation function which corresponds to each sampling cycle.
  • the results of the most recent autocorrelation function computation is stored in memory, whereby the signal peaks and signal period can be found.
  • the period of a fetal heartbeat ranges from approximately 300 to 1,500 milliseconds. Therefore, to compute an autocorrelation function over the range of the entire period of the heartbeat signal, it is necessary to find the autocorrelation function by varying the period of measurement from the minimum value of 300 milliseconds to the value of 1,500 milliseconds. In other words, it is necessary to change the phase difference variable ⁇ over the range of 300/T s to 1,500/T s in equation (2).
  • the autocorrelation function will have a maximum peak within this range when the phase difference variable ⁇ is set to the heartbeat signal period T, or to a period of time which is an interval multiple of the period T, the true period of the heartbeat signal can be found if the peak corresponding to the period ⁇ is detected.
  • the autocorrelation function computation is performed with each sampling cycle serving as a single division.
  • the shortest period of a fetal heartbeat signal is approximately 300 milliseconds.
  • the ccomputation of the autocorrelation function starts from the smallest possible value of the period of measurement, namely 300 milliseconds, in order to extract the results of measurement over a time interval which is equivalent to the period. That is, in the first sampling cycle, the autocorrelation function is first found with regard to the interval of 300 milliseconds corresponding to the minimum value of the fetal heartbeat period.
  • the autocorrelation function A(60) is found by the method used to find the autocorrelation function A( ⁇ ) in FIG. 3.
  • FIG. 4 shows a heartbeat signal.
  • Items of data f(1), f(2), f(3), f(4) . . . f(n) obtained by each sampling operation are stored in memory.
  • the value of A(60) is stored in memory for the purpose of comparison until the autocorrelation function is obtained in the next sampling cycle.
  • the computation is performed for the second sampling cycle, wherein the value of the phase difference variable is advanced by one to A(61).
  • the autocorrelation function is computed for a period of 305 milliseconds.
  • the computation of the autocorrelation function A(61) is carred out in essentially the same manner as the computation of the autocorrelation function A(60) and is not described again here.
  • the autocorrelation function A(61) obtained from the computation for the period of 305 milliseconds is compared with the autocorrelation function A(60) for the period of 300 milliseconds, as previously computed and stored in memory.
  • the system adapted herein computes an autocorrelation function for a certain value of the phase difference variable ⁇ in one sampling cycle, stores in memory solely the result of this computation, and then compares this result with the result of an autocorrelation function computation for a phase difference variable whose value is advanced by one count in the next sampling cycle. According, only the result of the autocorrelation function computation in the most recent cycle need be stored in memory.
  • the system of the present invention therefore makes it possible to reduce the required memory capacity of the correlation memory in comparison with the conventional system which requires that the correlation memory stores the results of each and every autocorrelation function computation covering the entire body of data spanning the range over which the phase difference variable ⁇ is varied in each sampling cycle.
  • the value which has previously been computed and stored for the preceding sampling cycle is compared with the value computed for the next sampling cycle.
  • the signal peaks are then detected by repeating this comparison process and examining the change in state. When there is a change in state from a larger value to a smaller value between two continuous sampling cycles, this indicates the detection of a peak in the first of the two cycles.
  • the comparison is made solely with the immediately preceeding computed value, in accordance with the description given above. However, it is obviously also possible to store computed values relating to several cycles and to perform a comparison among these values if desired.
  • a microprocessor can be employed owing to the reduction in the required storage capacity and the reduction in the number of computations. It therefore becomes possible to effect highly accurate autocorrelation function computations and system control.
  • the foregoing operation unfortunately detects not only an intrinsic peak corresponding to the signal period, but other peaks that generally tend to exist in the vicinity of the intrinsic peak. Therefore, in order to measure the period with a high order of precision, means must be provided to detect the intrinsic or true peak, which corresponds to the signal period, from among the several peaks that may exist.
  • a level check operation is performed on the basis of a minimum level determined to serve as a threshold value, and second, when a peak has been detected, the autocorrelation function computation is continued for a length of time which corresponds to the smallest period of measurement, to confirm that no peak larger than the detected peak exists in the interval over which the computation has been continued.
  • the level check operation comprises the steps of determining the threshold value of a level used in judging whether a peak has the potential of being a true peak, and then judging whether the level of a peak exceeds the threshold value, whereby it is decided whether the detected peak, which has the potential of being a true peak, should indeed be regarded as a true peak.
  • the threshold value is set to one-half the value of a peak employed in an immediately preceding measurement, namely to one-half the value of the most recent true peak, and only the peak whose level exceeds the set threshold value is judged to be a peak which has the potential of being a true peak.
  • the threshold value need not necessarily be set to one-half the value of the most recent true peak, but should be set to the optimum value chosen in accordance with the condition of the signal at that time.
  • the peak value of the true peak that indicates the period of the signal is influenced by the strength and waveform of the signal, noise poses a particular problem. Specifically, the lower the noise the larger and more distinct the true peaks present themselves, whereas the greater the noise the smaller the true peaks appear. In fact, the value of a true peak in the presence of considerable noise may even be smaller than a false peak in the vicinity of a true peak when there is little noise.
  • the threshold value must be set in accordance with the signal conditions that exist during peak detection.
  • the autocorrelation function computation is continued for a fixed interval of time following the detection of a peak, and a check is performed to determined whether a peak larger than the detected one exists within said fixed interval.
  • peaks obtained from an autocorrelation function include, in addition to a true peak that corresponds to the signal period, several peaks located in the vicinity of the true peak.
  • the true peak must be detected among the several peaks in order to measure the period correctly. Since the peaks in the vicinity of the true peak are generally located quite close to the true peak, it is possible to prevent the former peaks from being detected as the true peak by prolonging the autocorrelation function computation for a fixed interval following the detection of a peak and then by checking whether a peak larger than the detected one exists within said fixed interval. It should be noted that it is sufficient if the fixed interval is set to an interval of a value corresponding to the minimum period of measurement. Accordingly, in this embodiment, once a peak has been detected the computation of the autocorrelation function is prolonged for an interval that corresponds essentially to the minimum value of the period of measurement, namely to 300 milliseconds.
  • a peak P 3 of a smaller amplitude than peak P 2 , is found at a certain time t 31 within the 300-millisecond interval between the time t 12 at which P 2 is detected, and time t 22 .
  • the peak P 3 whose amplitude is smaller than that of peak P 2 , is not detected as a peak having the potential of being a true peak.
  • the peak P 2 obtained at time t 21 is detected as being a true peak indicative of the period when 300 milliseconds have passed starting from time t 21 , that is, when time t 22 has been reached.
  • the autocorrelation function computation ends and the period is calculated.
  • phase difference variable ⁇ of the true peak found in this manner corresponds to the period.
  • T s be the data sampling period
  • the correct period of the biosignal is measured in the manner described above.
  • peaks which are confirmed in this manner can be said to be those which have absolutely no possibility of indicating peaks of a period which is twice the true period.
  • period measurement starts from 300 milliseconds, which is the short possible period.
  • 300 milliseconds equivalent to the shortest possible period, is set as the true peak confirmation interval, so that the results of measurement can consequently be delivered in a time interval which is equivalent to the true period of the biosignal.
  • the true period is 500 milliseconds
  • the results of measurement will be output every 500 milliseconds.
  • the autocorrelation function computation proceeds at real-time on the correlation axis if the autocorrelation function computation interval coincides with the data sampling period, that is, because the correlation computation, for a length of time from the shortest period of the biosignal until a time represented by the sum of the shortest period and the true period, is performed within a time equivalent to the true period of the biosignal.
  • FIG. 6 shows, in simplified form, the construction of a period measurement apparatus for practicing the period measurement system described above in connection with FIGS. 3 through 5.
  • a transducer is brought into contact with the abdomen W of a female subject in order to detect the fetal heartbeat signal.
  • a sampling circuit 24 is connected to the transducer 22 through a preprocessing circuit 23.
  • the heartbeat signal detected by the transducer 22, after having its waveform suitably shaped by the preprocessing circuit 23, is sampled by the sampling circuit 24 at a predetermined sampling period and is subjected to an analog-to-digital conversion (AD conversion) by the sampling circuit.
  • the heartbeat signal therefore emerges from the sampling circuit 24 as a digital signal.
  • a data memory 26 is connected to the sampling circuit 24 and stores the sampled data obtained from the sampling circuit.
  • the data memory 26 is composed of a plurality of shift registers and operates as follows.
  • a multiplier 28 is connected to the data memory 26, and an adder is connected to the multiplier 28. More specifically, the data memory 26 or shift register comprises a 1-byte (8-bit) parallel register which is adapted to "shift in" the sampled data in digital form. It is so constructed that arbitrary positional data specified by signal line ad can be read out therefrom. Included in the data memory 26 are a random access memory (RAM) with a read and write capability, and a controller for the RAM.
  • RAM random access memory
  • the multiplier 28 and an adder 30 constitute a computation circuit for computing the autocorrelation function.
  • This circuit computes the autocorrelation function of a biosignal, namely the fetal heartbeat signal, by performing the computation specified essentially by equation (3) using the data stored in the data memory 26.
  • the computation of an autocorrelation function is performed in connection with a phase difference variable ⁇ of a certain value in each sampling cycle.
  • two items of data which represent two positions on the time axis separated from each other by the phase difference variable ⁇ , are produced by a control circuit 42 in a manner to be described later, and the two items of data are stored at two addresses in the memory section of the data memory 26 (the addresses giving the memory locations, which are indicated by the hatch marks in block 26 of FIG. 7).
  • the two items of stored data are multiplied and the product is entered in an accumulator located in the adder 30.
  • the number of multiplication operations for one phase difference variable ⁇ is n in equation (3), as will readily be understood from the foregoing description, so that the number of additions is n.
  • a peak detector 32 is connected to the adder 30 and is capable of storing a small quantity of data and of performing a comparison operation.
  • An input to the peak detector 32 is the value of the autocorrelation function calculated by the computation circuit constructed by multiplier 28 and adder 30.
  • the peak detector 32 stores the previously computed value of the autocorrelation function for one sampling cycle, and compares this value with the newly arrived computed value of the autocorrelation function for the next sampling cycle. The peak detector then stores the newly arrived computed value if it is larger than the previously stored computed value. Since the peak detector 32 need store only the computed value of the autocorrelation function for the most recent sampling cycle and the value of the phase difference variable ⁇ at that time, a small memory capacity will suffice.
  • the stored computed value for one sampling cycle is compared with the computed value of the autocorrelation function for the next sampling cycle by means of a comparator, thereby allowing the change in values for the two sampling cycles to be investigated.
  • the result of the comparison operation shows a transition from a higher to a lower value, this indicates the existence of a peak in the first of the two sampling cycles.
  • the peak detector 32 performs a comparison between a peak detection signal and a reference level. In order to set the reference level, use may be made of a level which is, for example, one-half the previously measured true peak value, as described earlier.
  • the peak detector 32 judges that the detected peak is a true peak and issues a true peak detection signal.
  • a period computation circuit 38 Connected to the peak detector 32 is a period computation circuit 38 which, upon receiving the true peak detection signal from a peak detector 32, computes the period on the basis of the value of the phase difference variable in the autocorrelation function at the time that the peak is obtained, said value being preserved in a register located within the peak detector.
  • a heartbeat computation circuit 40 Connected to the period computation circuit 38 is a heartbeat computation circuit 40 which computes the number of heartbeats on the basis of the period computed by the period computation circuit 38.
  • the heartbeat computation circuit 40 is connected to a control circuit 42, having a display device 44, such as an arrangement of light-emitting diodes (LED), connected thereto.
  • the display device 44 displays the number of heartbeats in the heartbeat signal on the basis of the signal obtained from the heartbeat computation circut 40 through the control circuit 42.
  • the control circuit 42 therefore is adapted to so control the signal from the heartbeat computation circuit 40 as to prevent it from entering the display device 44 on such occasions, thereby assuring that an erroneous heartbeat number will not be displayed.
  • the control circuit 42 is further adapted to deliver clock pulses to the sampling circuit 24, thereby to control the timing of the sampling operation effected by the sampling circuit.
  • the control circuit sends the multiplier 28 a signal, indicative of the value of the phase difference variable, upon each sampling operation.
  • the value of the phase difference variable successively advances as the sampling cycles progress, starting from a time which essentially corresponds to the minimum value of the hearbeat signal period.
  • the multiplier 28 is adapted to read, from the data memory 26, two items of data separated by the value of the phase difference variable designated by the signal from the control circuit 42, and to find the product of the two items of data.
  • the control circuit 42 sends a timing signal to the adder 30 which, on the basis of the timing signal, adds together the results of the computation operations executed by the multiplier 28.
  • the multiplier 28 and adder 30, under the control of the control circuit 42, read data from the data memory and compute the autocorrelation function essentially as shown by equation (3).
  • a reference level detector 46 Connected to the control circuit 42 is a reference level detector 46.
  • the latter in accordance with a timing signal delivered by the control circuit 42 at a suitable time interval, is adapted to detect the optimum reference level (zero level) for the purpose of attaching a positive (+) or negative (-) sign to the sampled data, and to send a signal indicative of the optimum reference level to the sampling circuit 24.
  • the reference level detector 46 is provided for the purposes of finding the optimum value for achieving this end. Specifically, the detector 46 finds the optimum value of the reference level by detecting the maximum value and minimum value, or the average value, of the data during sampling.
  • the peak detector 32 may have the construction shown in FIG. 8.
  • a memory 52 comprises two memory units, one for storing the value of the autocorrelation function, and the other for storing the value of the phase difference variable. More specifically, the memory 52, under the control of a write signal from a comparator 54, stores the value of the autocorrelation function computed by the adder 30, and the value of the phase difference variable obtained from the control circuit 42.
  • the comparator 54 is adapted to compare the newly computed value of the autocorrelation function obtained from the adder 30 and the most recent, largest computed value of the autocorrelation function previously stored in the memory 52, and to deliver the write signal to the memory 52 if the newly computed value of the autocorrelation function is the larger of the two values, whereby the contents of the memory 52 are replaced by the newly computed value of the autocorrelation function and by the value of the phase difference variable obtained from the control circuit 42.
  • the comparator 54 judges that a peak has been detected and therefore issues a signal.
  • the computed value of the autocorrelation function entered in the memory 52 is sent to a comparator 56 for checking the peak level.
  • the comparator 56 compares this value with a reference level received from a reference level generator 58.
  • the latter is set by the output timing of a counter 62 at such time that the preceding true peak is detected, whereby it stores a level equal to, say, one-half the value of the true peak detected by the preceding measurement. It is this level which the reference level generator delivers as the reference level. Obtaining one-half the value of a true peak is accomplished through the technique shown in FIG. 9.
  • this is accomplished by shifting the output data from the memory 52 one bit to the LSB (Least Significant Bit) side, and connecting the data to the comparator 56, which is a magnitude comparator. If the result of the comparison is such that the computed value of the autocorrelation function stored in the memory 52 is of a level that exceeds the reference level, the comparator 56 issues a signal.
  • An AND gate 60 takes the logical product of the outputs from the comparators 54, 56. A positive-going transition in the output of the AND gate 60 resets the counter 62 and sets the value of the phase difference variable ⁇ , which has been stored in the memory 52, in a register 64.
  • the counter 62 When the clock pulses being counted by the counter 62 reach a number which corresponds to a fixed time period, such as 300 milliseconds, the counter issues a signal. This output signal from the counter 62 indicates that a true peak has been detected, so that the value of ⁇ which has been set in the register 64 is delivered to the period computation circuit 38.
  • the latter circuit computes the period by taking the product of the variable ⁇ and the sampling period arriving from the control circuit 42 on a signal line. By way of example, if the sampling period is five milliseconds and ⁇ is 60 milliseconds, the period is computed as being 300 milliseconds.
  • the obtained period is delivered to the heartbeat counter circuit 40 where the number of heartbeats for a period one minute is found by dividing 60 ⁇ 10 3 (ms) by the period (ms).
  • the number of heartbeats found in this manner is then applied to control circuit 42 and displayed on the display device 44 under the control of the control circuit.
  • measurement of a biosignal period is performed through the steps of computing an autocorrelation function for a certain value of the phase difference variable ⁇ in one sampling cycle of the biosignal, changing the value of the phase difference variable ⁇ on the time axis in conformance to the progress of the sampling cycles, computing an autocorrelation function in each sampling cycle, storing solely the result of the autocorrelation function computation for the initial cycle of two consecutive sampling cycles, comparing this result with the result of the autocorrelation function computation for the following cycle, and detecting a peak from the increase and decrease in the result of comparison, whereby the period of the biosignal is measured.
  • Such an arrangement makes it possible to greatly reduce the storage capacity for the results of the autocorrelation function computations, and to eliminate meaningless autocorrelation computations for long intervals of time that may be two or three times as long as the actual biosignal period, thereby allowing data to be processed on an approximately real-time basis.
  • the correct period can be measured through the steps of beginning the autocorrelation function computation essentially from the minimum value of the period of biosignal measurement, continuing the autocorrelation computation for an interval corresponding to said minimum value following the detection of a peak, and confirming that there is no peak larger than the initial peak in said interval corresponding to the minimum value measured from the point of initial peak detection, thereby to detect that the initial peak is a true peak.
  • the correct period can be measured through the steps of beginning the autocorrelation function computation essentially from the minimum value of the period of biosignal measurement, continuing the autocorrelation computation for an interval corresponding to said minimum value following the detection of a peak, and confirming that there is no peak larger than the initial peak in said interval corresponding to the minimum value measured from the point of initial peak detection, thereby to detect that the initial peak is a true peak.
  • the invention since the range of autocorrelation function computation is restricted to an area from substantially the minimum value mentioned above to a range of values represented by the sum of the true biosignal period and confirmation interval (such as said minimum value), the invention has the effect of eliminating meaningless computations and of permitting real-time processing.
  • the results of measurements can be delivered at a time interval which is equivalent to the period of the signal undergoing measurement.

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JP55-97820 1980-07-17
JP9782180A JPS5722737A (en) 1980-07-17 1980-07-17 Cycle measuring system
JP9782080A JPS5722736A (en) 1980-07-17 1980-07-17 Cycle measuring system
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US4562846A (en) * 1983-09-15 1986-01-07 Duke University System and process for monitoring myocardial integrity
US4732157A (en) * 1986-08-18 1988-03-22 Massachusetts Institute Of Technology Method and apparatus for quantifying beat-to-beat variability in physiologic waveforms
US5241473A (en) * 1990-10-12 1993-08-31 Ken Ishihara Ultrasonic diagnostic apparatus for displaying motion of moving portion by superposing a plurality of differential images
US5558096A (en) * 1995-07-21 1996-09-24 Biochem International, Inc. Blood pulse detection method using autocorrelation
WO1997005821A1 (fr) * 1995-08-10 1997-02-20 Pentavox Kft. Procede et appareil pour mesurer le rythme cardiaque d'un foetus et sonde electroacoustique pour capter les sons provenant du coeur d'un foetus
WO2000024466A1 (fr) * 1998-10-23 2000-05-04 Varian Medical Systems, Inc. Procede et systeme de declenchement physiologique predictif d'une radiotherapie
US6115624A (en) * 1997-07-30 2000-09-05 Genesis Technologies, Inc. Multiparameter fetal monitoring device
US6279579B1 (en) 1998-10-23 2001-08-28 Varian Medical Systems, Inc. Method and system for positioning patients for medical treatment procedures
US6477476B1 (en) * 1999-12-06 2002-11-05 Koninklijke Philips Electronics N.V. Periodic-signal analysis via correlation
US20040005088A1 (en) * 1998-10-23 2004-01-08 Andrew Jeung Method and system for monitoring breathing activity of an infant
US6690965B1 (en) 1998-10-23 2004-02-10 Varian Medical Systems, Inc. Method and system for physiological gating of radiation therapy
US20040138557A1 (en) * 2002-10-05 2004-07-15 Le Toan Thanh Systems and methods for improving usability of images for medical applications
US20050054916A1 (en) * 2003-09-05 2005-03-10 Varian Medical Systems Technologies, Inc. Systems and methods for gating medical procedures
US20050053267A1 (en) * 2003-09-05 2005-03-10 Varian Medical Systems Technologies, Inc. Systems and methods for tracking moving targets and monitoring object positions
ES2232223A1 (es) * 2002-03-26 2005-05-16 Osatu, S. Coop. Metodo para la determinacion de la frecuencia de forma de onda de una señal ecg.
US20050119560A1 (en) * 2001-06-26 2005-06-02 Varian Medical Systems Technologies, Inc. Patient visual instruction techniques for synchronizing breathing with a medical procedure
US6937696B1 (en) 1998-10-23 2005-08-30 Varian Medical Systems Technologies, Inc. Method and system for predictive physiological gating
US20050201613A1 (en) * 1998-10-23 2005-09-15 Hassan Mostafavi Single-camera tracking of an object
US20050241362A1 (en) * 2002-08-26 2005-11-03 Hans-Dieter Oberle Method and device for detecting period length fluctuations of periodic signals
US20060074305A1 (en) * 2004-09-30 2006-04-06 Varian Medical Systems Technologies, Inc. Patient multimedia display
US20070053494A1 (en) * 1998-10-23 2007-03-08 Varian Medical Systems Technologies, Inc. Systems and methods for processing x-ray images
US20070167847A1 (en) * 2006-01-19 2007-07-19 Guglielmino Michael F Method and device for using a physiological parameter to express evolution
US20100061596A1 (en) * 2008-09-05 2010-03-11 Varian Medical Systems Technologies, Inc. Video-Based Breathing Monitoring Without Fiducial Tracking
US20100063419A1 (en) * 2008-09-05 2010-03-11 Varian Medical Systems Technologies, Inc. Systems and methods for determining a state of a patient
US20100158198A1 (en) * 2005-08-30 2010-06-24 Varian Medical Systems, Inc. Eyewear for patient prompting
US20110040499A1 (en) * 2008-03-31 2011-02-17 Jfe Steel Corporation Apparatus for detecting periodic defect and method therefor
US20110185584A1 (en) * 2007-05-21 2011-08-04 Snap-On Incorporated Method and apparatus for wheel alignment
US20130345585A1 (en) * 2011-03-11 2013-12-26 Koninklijke Philips N.V. Monitoring apparatus for monitoring a physiological signal
US20180020990A1 (en) * 2016-07-20 2018-01-25 Samsung Electronics Co., Ltd. Apparatus and method for extracting feature of bio-signal, and apparatus for detecting bio- information
US9936888B2 (en) 2010-10-14 2018-04-10 Murata Manufacturing Co., Ltd. Pulse period calculation device and biosensor equipped with the same

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EP0442011A1 (fr) * 1990-02-15 1991-08-21 Hewlett-Packard GmbH Sonde, appareil et méthode pour la mesure extracorporelle du taux d'oxygène
CN112869724B (zh) * 2021-01-19 2022-04-22 西安交通大学 一种基于多通道被动式采集信号的胎儿健康监测仪

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US4562846A (en) * 1983-09-15 1986-01-07 Duke University System and process for monitoring myocardial integrity
US4732157A (en) * 1986-08-18 1988-03-22 Massachusetts Institute Of Technology Method and apparatus for quantifying beat-to-beat variability in physiologic waveforms
US5241473A (en) * 1990-10-12 1993-08-31 Ken Ishihara Ultrasonic diagnostic apparatus for displaying motion of moving portion by superposing a plurality of differential images
US5558096A (en) * 1995-07-21 1996-09-24 Biochem International, Inc. Blood pulse detection method using autocorrelation
US6245025B1 (en) 1995-08-10 2001-06-12 Toeroek Miklos Method and apparatus for measuring fetal heart rate and an electroacoustic sensor for receiving fetal heart sounds
WO1997005821A1 (fr) * 1995-08-10 1997-02-20 Pentavox Kft. Procede et appareil pour mesurer le rythme cardiaque d'un foetus et sonde electroacoustique pour capter les sons provenant du coeur d'un foetus
US6115624A (en) * 1997-07-30 2000-09-05 Genesis Technologies, Inc. Multiparameter fetal monitoring device
US8788020B2 (en) 1998-10-23 2014-07-22 Varian Medical Systems, Inc. Method and system for radiation application
US20050201510A1 (en) * 1998-10-23 2005-09-15 Hassan Mostafavi Method and system for predictive physiological gating
US20070076935A1 (en) * 1998-10-23 2007-04-05 Andrew Jeung Method and system for monitoring breathing activity of a subject
US6621889B1 (en) 1998-10-23 2003-09-16 Varian Medical Systems, Inc. Method and system for predictive physiological gating of radiation therapy
US20040005088A1 (en) * 1998-10-23 2004-01-08 Andrew Jeung Method and system for monitoring breathing activity of an infant
US6690965B1 (en) 1998-10-23 2004-02-10 Varian Medical Systems, Inc. Method and system for physiological gating of radiation therapy
US20040071337A1 (en) * 1998-10-23 2004-04-15 Andrew Jeung Method and system for monitoring breathing activity of a subject
US10646188B2 (en) 1998-10-23 2020-05-12 Varian Medical Systems, Inc. Method and system for radiation application
US9232928B2 (en) 1998-10-23 2016-01-12 Varian Medical Systems, Inc. Method and system for predictive physiological gating
US7204254B2 (en) 1998-10-23 2007-04-17 Varian Medical Systems, Technologies, Inc. Markers and systems for detecting such markers
WO2000024466A1 (fr) * 1998-10-23 2000-05-04 Varian Medical Systems, Inc. Procede et systeme de declenchement physiologique predictif d'une radiotherapie
US7620146B2 (en) 1998-10-23 2009-11-17 Varian Medical Systems, Inc. Systems and methods for processing x-ray images
US6937696B1 (en) 1998-10-23 2005-08-30 Varian Medical Systems Technologies, Inc. Method and system for predictive physiological gating
US6279579B1 (en) 1998-10-23 2001-08-28 Varian Medical Systems, Inc. Method and system for positioning patients for medical treatment procedures
US20050201613A1 (en) * 1998-10-23 2005-09-15 Hassan Mostafavi Single-camera tracking of an object
US6959266B1 (en) 1998-10-23 2005-10-25 Varian Medical Systems Method and system for predictive physiological gating of radiation therapy
US7567697B2 (en) 1998-10-23 2009-07-28 Varian Medical Systems, Inc. Single-camera tracking of an object
US6973202B2 (en) 1998-10-23 2005-12-06 Varian Medical Systems Technologies, Inc. Single-camera tracking of an object
US6980679B2 (en) 1998-10-23 2005-12-27 Varian Medical System Technologies, Inc. Method and system for monitoring breathing activity of a subject
US20060004547A1 (en) * 1998-10-23 2006-01-05 Varian Medical Systems Technologies, Inc. Method and system for predictive physiological gating of radiation therapy
US7403638B2 (en) 1998-10-23 2008-07-22 Varian Medical Systems Technologies, Inc. Method and system for monitoring breathing activity of a subject
US7123758B2 (en) 1998-10-23 2006-10-17 Varian Medical Systems Technologies, Inc. Method and system for monitoring breathing activity of a subject
US20070053494A1 (en) * 1998-10-23 2007-03-08 Varian Medical Systems Technologies, Inc. Systems and methods for processing x-ray images
US7191100B2 (en) 1998-10-23 2007-03-13 Varian Medical Systems Technologies, Inc. Method and system for predictive physiological gating of radiation therapy
US6477476B1 (en) * 1999-12-06 2002-11-05 Koninklijke Philips Electronics N.V. Periodic-signal analysis via correlation
US20100289821A1 (en) * 2001-06-26 2010-11-18 Varian Medical Systems, Inc. Patient visual instruction techniques for synchronizing breathing with a medical procedure
US8200315B2 (en) 2001-06-26 2012-06-12 Varian Medical Systems, Inc. Patient visual instruction techniques for synchronizing breathing with a medical procedure
US20050119560A1 (en) * 2001-06-26 2005-06-02 Varian Medical Systems Technologies, Inc. Patient visual instruction techniques for synchronizing breathing with a medical procedure
US7769430B2 (en) 2001-06-26 2010-08-03 Varian Medical Systems, Inc. Patient visual instruction techniques for synchronizing breathing with a medical procedure
ES2232223A1 (es) * 2002-03-26 2005-05-16 Osatu, S. Coop. Metodo para la determinacion de la frecuencia de forma de onda de una señal ecg.
US7254502B2 (en) * 2002-08-26 2007-08-07 Infineon Technologies Ag Method and device for detecting period length fluctuations of periodic signals
US20050241362A1 (en) * 2002-08-26 2005-11-03 Hans-Dieter Oberle Method and device for detecting period length fluctuations of periodic signals
US7620444B2 (en) 2002-10-05 2009-11-17 General Electric Company Systems and methods for improving usability of images for medical applications
US20040138557A1 (en) * 2002-10-05 2004-07-15 Le Toan Thanh Systems and methods for improving usability of images for medical applications
US20050054916A1 (en) * 2003-09-05 2005-03-10 Varian Medical Systems Technologies, Inc. Systems and methods for gating medical procedures
US20050053267A1 (en) * 2003-09-05 2005-03-10 Varian Medical Systems Technologies, Inc. Systems and methods for tracking moving targets and monitoring object positions
US8571639B2 (en) 2003-09-05 2013-10-29 Varian Medical Systems, Inc. Systems and methods for gating medical procedures
US20060074305A1 (en) * 2004-09-30 2006-04-06 Varian Medical Systems Technologies, Inc. Patient multimedia display
US20100158198A1 (en) * 2005-08-30 2010-06-24 Varian Medical Systems, Inc. Eyewear for patient prompting
US9119541B2 (en) 2005-08-30 2015-09-01 Varian Medical Systems, Inc. Eyewear for patient prompting
US20070167847A1 (en) * 2006-01-19 2007-07-19 Guglielmino Michael F Method and device for using a physiological parameter to express evolution
US20110185584A1 (en) * 2007-05-21 2011-08-04 Snap-On Incorporated Method and apparatus for wheel alignment
US8401236B2 (en) 2007-05-21 2013-03-19 Snap-On Incorporated Method and apparatus for wheel alignment
US9008975B2 (en) * 2008-03-31 2015-04-14 Jfe Steel Corporation Apparatus for detecting periodic defect and method therefor
US20110040499A1 (en) * 2008-03-31 2011-02-17 Jfe Steel Corporation Apparatus for detecting periodic defect and method therefor
US20100063419A1 (en) * 2008-09-05 2010-03-11 Varian Medical Systems Technologies, Inc. Systems and methods for determining a state of a patient
US20100061596A1 (en) * 2008-09-05 2010-03-11 Varian Medical Systems Technologies, Inc. Video-Based Breathing Monitoring Without Fiducial Tracking
US10667727B2 (en) 2008-09-05 2020-06-02 Varian Medical Systems, Inc. Systems and methods for determining a state of a patient
US9936888B2 (en) 2010-10-14 2018-04-10 Murata Manufacturing Co., Ltd. Pulse period calculation device and biosensor equipped with the same
US20130345585A1 (en) * 2011-03-11 2013-12-26 Koninklijke Philips N.V. Monitoring apparatus for monitoring a physiological signal
US20180020990A1 (en) * 2016-07-20 2018-01-25 Samsung Electronics Co., Ltd. Apparatus and method for extracting feature of bio-signal, and apparatus for detecting bio- information

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FR2495330B1 (fr) 1985-01-25

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